Method of connecting commutator bars in a cross-linked commutator having additional parallel paths

ABSTRACT

A method of linking commutator bars of a commutator for a motor wherein N is the number of magnetic poles of the motor and N is an even integer greater than 2. The method include a) arranging a plurality of commutator bars to be generally equally spaced in a circular arrangement to define the commutator, each commutator bar having a tang extending therefrom, b) contacting an end of a continuous, insulated conductive member to a tang, c) moving the member to contact a second tang which is disposed at an angle of 720°/N from the previously contacted tang to form a link, and when N is greater than four, repeating this step until N/2−1 links are created, d) moving the member to contact a tang which is immediately adjacent to the second tang contacted in step (c) such that the member defines a bridging portion between the adjacent tangs, e) repeating steps (c) and (d) and until all tangs have been contacted by the member, and f) cutting the bridging portion between adjacent tangs.

This application is based on and claims the benefit of U.S. ProvisionalApplication No. 60/146,547, filed on Jul. 30, 1999.

FIELD OF THE INVENTION

This invention relates to multipole D.C. electric motors with lap-woundcoil configurations and, more particularly, to a commutator for amultipole motor having electrically cross-linked commutator bars.

BACKGROUND OF THE INVENTION

In a conventional multipole D.C. electric motor having a lap-wound coilconfiguration on the armature, for optimum motor performance, the numberof electrical brush pairs (1 positive and 1 negative) is half the numberof magnetic poles. Thus, a four magnetic pole motor has two sets ofbrush pairs or four brushes in total. The brushes are equally spacedaround the motor commutator and in the case of the four pole, four brushmotor, the brush spacing is an angle of 90°. The electrical polarity ofthe sequence of the brushes is positive, negative, positive andnegative, which ensures four equally balanced parallel circuits in thearmature for optimum motor operation. To apply electrical power to thefour brushes, the two positive brushes need to be interconnected and thetwo negative brushes need to be interconnected. A large brush hold isrequired with the associated electrical connections between theindividual brush pairs since the brushes are spaced at 90° from eachother.

Recently, it has been proposed to link commutator bars of a wave-woundmotor so as to reduce the number of brushes of the motor. However, thewinding process is difficult since it is a two-part process requiringindexing and requiring that the commutator links be wound onto thearmature with the armature windings. Furthermore, the resulting windingfrom the wave-wound process consumes much space since there is a greatdeal of wire between the lamination stack and the commutator.

Accordingly, there is a need to provide an improved commutator for alap-wound motor by having electrically cross-linked commutator barsconnected in a continuous winding process to provide additional parallelpaths and thus reduce the number of brushes in a multipole motor.

SUMMARY OF THE INVENTION

An object of the present invention is to fulfill the need referred toabove. In accordance with the principles of the present invention, thisobjective is obtained by a method which provides a commutator for alap-wound motor wherein N is the number of magnetic poles of the motorand N is an even integer greater than 2. The method includes arranging aplurality of commutator bars to be generally equally spaced in acircular arrangement. Sets of commutator bars which are disposed at anangle of 720°/N therebetween are electrically connected together suchthat each set of connected commutator bars is electrically isolated fromall other sets of connected commutator bars. A lap-winding is thenconnected to the commutator.

In accordance with another aspect of the invention, a method is providedto connect commutator bars of a commutator for a lap-wound motor,wherein N is the number of magnetic poles of the motor and N is an eveninteger greater than 2. The method includes arranging a plurality ofcommutator bars to be generally equally spaced in a circular arrangementto define a commutator. Each commutator bar has a tang extendingtherefrom. The method further includes:

a) contacting an end of a continuous, conductive member to a tang,

b) moving the member to contact and link a tang which is disposed at anangle of 720°/N from the previously contacted tang and if N is greaterthan four, repeating this step until N/2−1 links are created,

c) moving the member to contact a tang which is immediately adjacent tothe last tang contacted in step b) such that the member defines abridging portion between the adjacent tangs,

d) repeating step c) until all tangs have been linked by said member,and

e) cutting the bridging portion between said adjacent tangs, therebyelectrically connecting certain of said tangs while electricallyisolating said certain tangs from other electrically connected tangs.

Other objects, features and characteristics of the present invention, aswell as the methods of operation and the functions of the relatedelements of the structure, the combination of parts and economics ofmanufacture will become more apparent upon consideration of thefollowing detailed description and appended claims with reference to theaccompanying drawings, all of which form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a commutator provided in accordance with theprinciples of the present invention having cross-linked bar connections;

FIG. 2 is a plan view of a commutator for a four-pole motor provided inaccordance with the principles of the present invention showing awinding pattern to cross-link sets of commutator bars;

FIG. 3 is a plan view of a view showing a step of cutting a bridgingportion between adjacent commutator bars using a cutting instrument;

FIG. 4 is a plan view of hooked-shaped members forming from the cutbridging portion of FIG. 3;

FIG. 5 is a view of the commutator of FIG. 2 after cutting bridgingportions;

FIG. 6 is a cross-sectional view of the commutator of FIG. 5 taken alongthe line 6—6;

FIG. 7 is a top view of a brush card assembly of a motor of theinvention which employs a cross-linked commutator; and

FIG. 8 is a plan view of a printed circuit board for cross-linkingcommutator bars in accordance with a second embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

On a normal motor commutator, each individual commutator bar iselectrically isolated from every other commutator bar. The inventionprovides a motor commutator, generally indicated at 100, which, when anelectrical potential is applied to one of the commutator bars, that samepotential is generally simultaneously present on N/2 bars. Thecommutator bars are equally spaced in a circular arrangement to define acommutator. N is the total number of magnetic poles of the motor. Forexample as shown in FIG. 1, in the case of a four pole motor, there are4/2 or a minimum of two commutator bars A and B electrically connectedtogether via connection structure 120 and separated by an angle of 720/Nor, in this case, 180°. The connection structure joins tangs A′ and B′of commutator bars A and B, respectively. All the bars on the commutatorwhich are disposed at an angle of 720/N (180°) from each other areconnected together. Thus, bars C and D are also electrically connectedtogether via connection structure 120 at tangs C′ and D′. In theillustrated embodiment, the connection structure 120 is preferably asingle, solid strand of insulated copper wire but may be of anyinsulated, electrically conducting material, such as bars, etc. Eachindividual connected set of commutator bars (A and B) is electricallyinsulated from all other interconnected sets of commutator bars (C andD). For motors with poles greater than four, [(N/2)−1] links are createdin each set to join N/2 commutator bars at relative angles of 720/Ndegrees.

When the above-described commutator 100 is used in a four pole,lap-wound armature style motor, advantageously, only two brushes arerequired, one at the positive potential and one at the negativepotential. By cross-linking sets of commutator bars, the second twopositive and negative brushes of the conventional four pole, lap-woundmotor are not required since the electrical paths are created by thecross-linked connection structure 120. The motor employing thecommutator 100 of the invention operates in the same manner and with thesame characteristics as the conventional four brush system of the fourpole motor.

With regard to commutators of the invention to be used on multipolemotors with an even number of magnetic poles equal to or greater thanfour in number, the following will apply:

Number of magnetic poles: N (= even integer >2) Minimum number ofcommutator bars: N Minimum number of sets of bars to be N/2 electricallyconnected: Angle between connected commutator bars: 720°/N Angle betweenmotor brushes: (360°/N)(1,3,5,...[N − 1])

With regard to the spacing or angle between brushes, for example, in asix-pole motor, the brushes may be spaced 60 or 180 degrees apart and inan eight-pole motor, the brushes may be spaced 45 or 135 degrees apart.

A method of connecting commutator bars together to define the commutatorof the type described above will be apparent with reference to FIGS. 2-6and the following description. The process electrically connectscommutator bar sets (for example, bars 140 and 142 in FIG. 2) on a fourpole commutator 100′ at angles of 720/N from each other but electricallyisolated from all other interconnected commutator bar sets of thecommutator 100′. In the embodiment of FIG. 2, the commutator 100′ is fora four-pole motor. Thus, N=4 and 720°/N is 180°.

The method includes providing a commutator 100′ with tangs formed oneach commutator bar and then hooking, sequentially, a connectionstructure 120 around sets of tangs as illustrated in FIG. 2.

FIG. 2 shows the inventive hooking sequence for a four pole motor with atwenty slot commutator 100′ having twenty tangs. The tangs are numbered1-20 in FIG. 2. A continuous wire defining the connection structure 120is used to link sets of commutator bars via the tangs. First, end 152 ofthe wire 120 is secured to tang number 1. The hooking sequence is fromtang 1 to 2, 2 to 3, 3 to 4, 4 to 5, 5 to 6, and so on until tang 19 isconnected or linked to tang 20. The other end 154 of the wire 120 issecured to tang number 20 to complete the cross-linking.

With reference to FIGS. 3 and 4, after the hooking sequence iscompleted, a cutting sequence is initiated. During the cutting sequence,the bridging portion 148 of the connection structure 120 between tangs2-3, 4-5, 6-7, 8-9, 10-11, 12-13, 14-15, 16-17 and 18-19 is cut andformed into a hook shape. As shown in FIG. 3, a cutting instrument 158,preferably a knife, is used to cut the bridging portion 148. Thereafter,as shown in FIG. 4, two hooked-shaped members 150 are formed from thecut bridging portion. The completed cross-linked commutator 100′ isshown after the cutting process in FIGS. 5 and 6. The dashed line inFIG. 6 represents the extent of the wire pile after cross-linking. Aconventional lap-winding can now be connected to the cross-linkedcommutator 100′ in the conventional manner requiring no changes to theconventional winding tools for lap-wound armatures. Thus, thelap-winding is performed independently from linking of the commutatorbars. With this structure and as shown in FIG. 7, the number of brushes160 of a brush card assembly 161 of the motor 162 is reduced to two inall cases regardless of the value of N.

Although the method of joining sets of commutator bars has beendescribed with regard to a twenty slot commutator, it can be appreciatedthat the method applies to connecting sets of commutator bars ofcommutators having fewer than or more than twenty bars.

Summarizing, wire first contacts a first tang and then the wire is movedto contact and link a second tang which is disposed at an angle of720°/N from the first tang. For motors with poles greater than 4 (N>4)the pattern is repeated until [(N/2)−1] links are created. The wire isthen wrapped around an adjacent tang immediate clockwise of the lasttang hooked, such that the wire defines a bridging portion between thosetwo tangs. This pattern is repeated until all tangs have been linked. Ina four pole motor, this bridging portion is between the second and thirdtangs thereby electrically connecting the first and second tangs and thethird and fourth tangs with the first and second tangs beingelectrically isolated from the third and fourth tangs. In motors withpoles greater than four, the first group of N/2 tangs are electricallyconnected an angle of 720/N. After the [(N/2)−1] links are created, thewire is connected to an adjacent tang. The wire bridging portion betweenthis adjacent tang and the previous 720/N tang is cut. Thus the secondset of [(N/2)−1] linked tangs will be electrically isolated from thefirst set of tangs.

The insulation on the copper wire of the connection structure 120 isstill present at the commutator bar hooks 150 (FIG. 4) and remains thereuntil after the commutator 100′ is placed on the armature stack assemblyand the insulated wire coils are wound onto the armature and hookedsequentially to the commutator 100′. The armature coils and thecommutator bar interconnecting wires are fused by fusion welding to thecommutator bars in the conventional manner by a combination of heat andpressure. The insulation of the copper wires is vaporized locally duringthis process causing the complete electrical connections to be made.

With reference to FIG. 8, connection structure 120′, generally indicatedat 120′, is shown in accordance with a second embodiment of theinvention. The connection structure 120′ comprises a two-sided printedcircuit board. The circuit board 120′ is arranged at one end of acommutator (not shown) with the motor shaft (not shown) extendingthrough a central hole 200 in the circuit board 120′. One side of thecircuit board 120′ includes a plurality of radially extending bars 210having distal ends 212. Each distal end 212 extends beyond the outsidediameter of the commutator and includes a cut-out 214. The cut-outs 214receive the commutator bar hooks so as to be electrically connected tothe distal ends 212. The radial bars 210 may be traces on the printedcircuit board 120′ or may be stamped pieces bonded to the circuit board.

A series of concentric rings 216 traces are defined on the second sideof the printed circuit board 120′. Sets (in the illustrated embodimentpairs) of radial bars 210 are electrically connected by attaching theradial bars 210 in each set to a single ring 216 using throughconnectors 218 (vias). In the illustrated embodiment, the throughconnectors 218 are arranged in a spiral pattern on the printed circuitboard 120′, connecting each radial bar to a corresponding ring 216,which, in turn, is connected to another radial bar 180 degrees apart.For example, in the illustrated embodiment, radial bar 210′ is connectedwith radial bar 210″ via ring 216′. Thus, the connectors 218electrically joining a set of radial bars are disposed substantially ata common radius from a center 220 of the printed circuit board 120′,with connectors 218 electrically joining one set of radial bars beingdisposed on a radius from the center 220 which is different from anotherset of joined radial bars.

It can be appreciated that sets of three or more radial bars may beconnected using this method. As in the first embodiment, the number ofbrushes of the motor is reduced to two in all cases regardless of thevalue of N.

The foregoing preferred embodiments have been shown and described forthe purposes of illustrating the structural and functional principles ofthe present invention, as well as illustrating the methods of employingthe preferred embodiments and are subject to change without departingfrom such principles. Therefore, this invention includes allmodifications encompassed within the spirit of the following claims.

What is claimed is:
 1. A method of linking commutator bars of acommutator for a motor wherein N is the number of magnetic poles of themotor and N is an even integer greater than 2, the method including: a)arranging a plurality of commutator bars to be generally equally spacedin a circular arrangement to define said commutator, each commutator barhaving a tang extending therefrom, b) contacting an end of a continuous,insulated conductive member to a tang, c) moving the member to contact asecond tang which is disposed at an angle of 720°/N from the previouslycontacted tang to form a link, and when N is greater than four,repeating this step until N/2−1 links are created, d) moving the memberto contact a tang which is immediately adjacent to the second tangcontacted in step (c) such that the member defines a bridging portionbetween the adjacent tangs, e) repeating steps (c) and (d) until alltangs have been contacted by said member, and f) cutting the bridgingportion between said adjacent tangs.
 2. The method according to claim 1,further including forming the cut bridging portion into twohooked-shaped members.
 3. The method according to claim 1, wherein saidmember is an insulated copper wire.
 4. The method according to claim 1,wherein said bridging portion is cut by a knife.
 5. The method accordingto claim 1, further comprising connecting a lap-winding to thecommutator by fusing thereby vaporizing insulation from the conductivemember at the tangs.
 6. The method according to claim 1, wherein N isfour.